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Topic Title: §706 - Conducting Locations with Restricted Movement
Topic Summary: Defining the scope
Created On: 21 March 2017 08:15 PM
Status: Read Only
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 §706 - Conducting Locations with Restricted Movement   - jammyc - 21 March 2017 08:15 PM  
 §706 - Conducting Locations with Restricted Movement   - mapj1 - 21 March 2017 09:14 PM  
 §706 - Conducting Locations with Restricted Movement   - mapj1 - 21 March 2017 09:39 PM  
 §706 - Conducting Locations with Restricted Movement   - jammyc - 22 March 2017 10:23 AM  
 §706 - Conducting Locations with Restricted Movement   - mapj1 - 22 March 2017 11:02 AM  
 §706 - Conducting Locations with Restricted Movement   - jammyc - 23 March 2017 01:59 PM  
 §706 - Conducting Locations with Restricted Movement   - OMS - 23 March 2017 02:14 PM  
 §706 - Conducting Locations with Restricted Movement   - jammyc - 24 March 2017 02:02 PM  
 §706 - Conducting Locations with Restricted Movement   - OMS - 24 March 2017 06:56 PM  
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 21 March 2017 08:15 PM
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jammyc

Posts: 30
Joined: 25 November 2009

Hi all,

One of my clients has asked for comments on an installation they operate and I am not sure if it falls within the scope of section 706, and therefore if Obstacles are permitted or not as a measure.

The installation is built into a re-purposed shipping container, with metal floors, walls etc. Most of the volume is occupied by steel-clad equipment, but there is an access corridor at one end which is approx 55cm wide and maybe 1.8m long. It's not a gangway as there's no switchgear or controlgear in there (all the equipment faces outward), but periodic access is required to inspect the MET and visually check for dust, rodents etc the inside of the container... and an exposed busway protected by a partial barrier which does meet the physical and procedural requirements for an Obstacle.

Besides the bars behind an obstacle there are some other LV items which rely on ADS such as fans (overhead), and some ELV control circuits.

Having had a look in there I am inclined to apply §706 as it is cramped to access. For example if you crouch to inspect the MET you are forced against the metal on each side, and when wearing full PPE per site rules you can only exit sideways. Before I do though I'd like to confirm that I'm not being overly conservative, as the scope seems to be open to interpretation and if it does apply rectification works and an expensive outage will be required.

If, by the letter, it doesn't apply, a set of carefully considered RAMS would be needed anyway, but there would be a little bit more latitude on the balance between procedural controls and physical measures. This might well end up at the same requirement, of course, but the discussion would be different (not least regarding finger-pointing at suppliers).

Thanks in advance.
Regards,
James
 21 March 2017 09:14 PM
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mapj1

Posts: 9349
Joined: 22 July 2004

sounds like it might apply - is there anything in there that is actually an unusual hazard - and do folk go in there to use mains powered tools ? if so then in this day and age to use battery power is probably a better bet whenever possible, less risk of snagged cables or shocks from damaged kit.

Assuming this section does apply, then as regards fixed equipment running off the mains, the normal approaches of either double insulation or metal covers and earthing are normally considered enough, but a bit more thought may be needed than the usual fire and forget...

for example , are there any activities like opening covers up for maintenance, that could expose live terminals, do folk go near or need to squeeze past that exposed busway you mention, (and if so what voltage and PSSC/ arc potential - there is a huge difference between current limited, or single phase 220v and 690 and up in this regard)
Then are there additional hazards like water or anti-freeze , that may increase body conductivity - perhaps if a cooling system leaks, or can there be extreme heat, that may encourage sweaty operators to go in more lightly clothed than normal ?
If so a 'turn off and make safe before going in' regime will be needed, maybe interlocks or alarms, or just some kind of buddy scheme with no lone working, which is quite common with experimental kit..

you mention PPE - generica rules may not be appropriate for that setting and may need to be varied - in the same way that ear defenders are a good idea, until you really need to hear if something is leaking, or about to run you over, it may be that alternate footwear or headwear may be needed for some specific task, if the normal issue increases the risk of getting stuck.

As someone who has in the past squeezed into a box along-side a water filled system with the water designed to circulate at 11kV, it is fair to say that most people's ideas of what is either possible or sensible sometimes need careful re-calibration, ideally from someone actually doing the damn job, and looking the regs alone without the background info, and applying some serious engineering judgement, may not be enough.

I expect Paul will be along in a minute to ask if it is covered by the machinery directive...

-------------------------
regards Mike


Edited: 21 March 2017 at 09:37 PM by mapj1
 21 March 2017 09:39 PM
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mapj1

Posts: 9349
Joined: 22 July 2004

second thought - is it safer not to inspect the met, after all who says it needs inspecting at all and why, but to verify continuity from outside, and can the rodent check be done by camera rather than human entry ?

-------------------------
regards Mike
 22 March 2017 10:23 AM
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jammyc

Posts: 30
Joined: 25 November 2009

Thanks for the quick reply Mike! (c:

The biggest unusual hazard is the bars, which are directly attached to a the LV side of a 2MW/33kV transformer limited by the HV fuse only (there are LV ACBs but this bar is effectively the incoming supply so we're upstream of them) so Ipscc is substantial. That said it's arranged as IT for operational reasons which does incidentally give some protection from first fault. On the other hand, they are hidden behind a steel sheet which does give protection from the front, but there are ledges above eye level where tools could fall in and onto them (and frankly you'd probably not know they were there unless you did that). Otherwise it's only lighting, cooling fans, etc, so if one fails one might be opening up covers for testing.

It's a purely electrical building so there's nothing like water, chemicals, fumes or the like to exacerbate any problems. Nothing I can think of will require power tools while the system's live, only hand tools and test equipment.

You're right, most checks could be done from outside with a (long) selfie stick and a suitable set of lanyards to stop bits falling in. I have raised the idea of cameras is it would be a cheap solution - pleased to see someone else suggest it though; I did wonder if I was running away with myself with that one.

Making the whole thing dead is an option, but because the bars are fed directly from a transformer it requires a SAP for HV switching, which isn't practical for routine maintenance, and to prove it you'd need to remove covers which could be taken as exposing oneself to greater hazard (unless I get them to fit fused test points, but perhaps that's getting OTT). Also, the resulting outage has a big cost penalty (which is not a reason to be unsafe, but it does mean we should try to avoid it). Does the whole installation need to be switched off if a 'stat relay has stuck? Maybe it does. For more intensive annual work it is unavoidable.

PPE-wise, the company generally prefers operatives to don arc suits, albeit relatively low energy ones, in this type of scenario. To persuade them otherwise will be quite a job.

I did go in there with their site maintenance electrician - i.e. the guy who'd be doing this every month - and he was reasonably comfortable once we'd talked through a few improvements along the lines you've suggested. It was only after writing up the report that I wondered if the BYB would force us down a particular course of action.

Ta,
James
 22 March 2017 11:02 AM
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mapj1

Posts: 9349
Joined: 22 July 2004

Sounds safer than I imagined it might be, and you are well on the way to a good solution.

But still a serious PSSC on those unfused bars. (2MVA , err, say 3kA/phase of load current , you may expect PSSC of ten to twenty times that, dunno ?) That would be one $%^£$ of a loud bang, and potentially some serious pressure wave depending how long disconnection takes, - and where would the products of such an explosion go ? - note that indoor substation buildings are carefully designed to blow walls or roof off in a specific way to vent in fault levels that are not much different.
Off the end of what I do, but DNO folk may be able to comment on how fast the HV side would go off.

How hard would it be to add a section of grid like a shopping basket to discourage stuff from being put where it could be at risk off falling in - I presume it cannot be closed fully for thermal reasons and under what conditions are folk doing that needs putting tools up there anyway ?

Is there isolation for the fans and other loads they supply to allow them to be serviced.- is that just the ACB ? Clear marking of which covers require HV isolation and which are safe with LV only..

non-flammable clothing IS sensible - I was not sure if you had meant Florence boots, space helmet and lead underwear - sometimes the H and S PPE folk get a bit carried away and specify some odd site-wide rule that needs relaxing on a task specific basis (plimsoles for walking on some surfaces where boots don't grip for example)

So yes, it probably is a confined location, and if not then very nearly, but with some thought, apart fro the busbars, the risk should be manageable, and you seem to be well on the way.

-------------------------
regards Mike


Edited: 22 March 2017 at 11:15 AM by mapj1
 23 March 2017 01:59 PM
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jammyc

Posts: 30
Joined: 25 November 2009

Yes, the PSCC is quite large. Rough figures (still waiting on confirmation of network fault level, but in the sticks so not very high) said just shy of 50kA for bolted 3ph. Access requires the container doors to be open anyway so that should be sufficient for blast relief (but it's a good point and I'll make sure it's covered).

Extra panelling is probably the way forward. You're right I don't want to fully enclose the bars for thermal reasons (and it'll impede the lighting which is in a silly place). However I might end up spec'ing as IP2X grille rather than a basket type a) Because some of those ledges really do look tempting for screwdrivers and b) it saves questions later (I can just call it a proper Barrier then). It's a little bit of a faff due to kit mounted on the ceiling (lights, smoke detector etc) but eminently do-able at the next planned outage.

Re the fans (and other aux circuits), they're served by an isolation transformer behind an ACB and equipped with DP isolation accessible from outside. Proper labelling is on the To Do list also.

Thanks again,
James
 23 March 2017 02:14 PM
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OMS

Posts: 22359
Joined: 23 March 2004

I'm presuming the transformer is outside the ISO - so those busbars are exposed externally as well - and pass through the metal walls of the ISO via insulated bushings ?

Personally speaking, If I was letting relatively unskilled persons in there (lamp changes, AFD testing, etc) then I would want the whole of the power train built to an equivalent of BS EN 61439 and at 50kA 3 seconds. Being in close proximity to a 50kA, 2MVA busbar isn't sensible

Have you considered swapping out the bare busbars with a commercial encapsulated bus bar system (see my first point above) from the TX LV spill box through to the switchboard input cubicle

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 24 March 2017 02:02 PM
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jammyc

Posts: 30
Joined: 25 November 2009

Originally posted by: OMS

I'm presuming the transformer is outside the ISO - so those busbars are exposed externally as well - and pass through the metal walls of the ISO via insulated bushings ?

Yes it is outside but the bars transition internally to parallel sets of cabling glanded (non-ferrous plate) through the wall, then on some heavy duty ladders (not done the calcs but they do look good for the fault) to the spill box


Personally speaking, If I was letting relatively unskilled persons in there (lamp changes, AFD testing, etc) then I would want the whole of the power train built to an equivalent of BS EN 61439 and at 50kA 3 seconds. Being in close proximity to a 50kA, 2MVA busbar isn't sensible

Access will be controlled and only allowed to electricians with system-specific training... But yes, I agree it would have been far preferable to build the system better in the first place. Sadly I wasn't involved at that stage.


Have you considered swapping out the bare busbars with a commercial encapsulated bus bar system (see my first point above) from the TX LV spill box through to the switchboard input cubicle

No I hadn't. I do see your point for a new build but the cost of doing that retrospectively including the lost service and the like would probably be prohibitive if we think we can make it safe with simpler measures. To be fair, they are on the other side of a sheet of steel, and unless you drop something in (which additional barriers plus signage plus limitations on access should prevent) you'd not know about it.

James
 24 March 2017 06:56 PM
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OMS

Posts: 22359
Joined: 23 March 2004

You would know all about it if those bubars short and you have an ionising flashover within the enclosure - keep in mind you need the HV protection to operate

OMS

-------------------------
Let the wind blow you, across a big floor.
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